1. Field of the Invention
This invention relates to a cover stock for golf balls and golf balls having a cover of the cover stock.
2. Prior Art
Ionomer resins, which are metal ion-crosslinked products of ethylene-.alpha.,.beta.-unsaturated carboxylic acid copolymers, are often used as the cover stock for two-piece golf balls and wound golf balls because of their resilience, impact durability, and cut resistance. Since the ionomer resins, however, have a higher hardness than balata rubber which is well known as the cover stock in the golf ball art, the ionomer covered golf balls give an unpleasant feel when hit and are less controllable because of difficulty to impart an appropriate spin on iron shots.
One cover stock proposed to solve this problem is a blend of an ionomer resin having a very low hardness, that is, a metal ion-crosslinked product of an ethylene-.alpha.,.beta.-unsaturated carboxylic acid-unsaturated carboxylate terpolymer with a metal ion-crosslinked product of an ethylene-.alpha.,.beta.-unsaturated carboxylic acid copolymer. Using this cover stock, golf balls having a relatively soft cover, a good feel when hit, and ease of control are obtainable. This cover stock, however, is insufficient in flight distance because the metal ion-crosslinked product of an ethylene-.alpha.,.beta.-unsaturated carboxylic acid-unsaturated carboxylate terpolymer is less resilient, and blending with the metal ion-crosslinked product of an ethylene-.alpha.,.beta.-unsaturated carboxylic acid copolymer cannot compensate for this loss.
JP-A 14879/1985 and 145160/1985 propose to use blends of an ionomer resin and polyethylene as the cover stock. Since the ionomer resin is less compatible with polyethylene, these blends lack the uniformity of dispersion and hence, durability. Because of the relatively high hardness of polyethylene, the balls do not necessarily give a satisfactory feel when hit.
JP-A 140831/1997 discloses a golf ball-forming stock material comprising a metallocene-catalyzed polyolefin alone or in admixture with an ionomer resin. In the former case, the feel and resilience of golf balls are not fully satisfactory. In the latter case, the feel and resilience of golf balls are improved, but the stock material sometimes lacks uniformity of dispersion and hence, durability due to the low compatibility between the metallocene-catalyzed polyolefin and the ionomer resin.